Page 288. Paragraph three, fifth line, the substantive " cerebello-
spinal fasciculus" should have "posterior" prefixed so as to read
posterior cerebello-spinal fasciculus. This is a necessary varia-
tion from the BNA and applies wherever the phrase is found.

Page 291. Last line, there should be added a fifth item, viz., (e)
the medullarv striae.

ERRATA. XXXV

Page 319. Fifth line, common sensory should be added under
intermediate nerve.

Page 35 ! Paragraph three, third item, (3) should be omitted,
as no posterior root-fibers decussate. Intrinsic fibers only cross
through the gray commissure (Mott and Russell).

Page 358. To the last sentence should be added: and according
to Sir Victor Horsley has to do with locomotion (Brain, 1906).

Page 410. Fourth line, "callosal fissure" should be callosal
sulcus.

BRAIN AND SPINAL CORD.

CHAPTER I.

THE MENINGES OF THE BRAIN.

(Meninges Encephali.)

Three membranes invest the brain and spinal cord. They
are, from without inward, the dura mater, the arachnoid, and
the pia mater. Each membrane forms a protecting sheath for
the cerebral or spinal nerves piercing it.

THE DURA MATER OF THE BRAIN.

(Dura Mater Encephali.)

Structure and Relations. It is a very dense and inelastic
membrane composed of white fibrous and yellow elastic tissue
lined with flat endothelial cells, which constitute its internal
surface. In children it is closely adherent to the cranial bones of
which it forms the real periosteum; but it is attached chiefly at
the foramina and along the sutures in adults. The dura of the
brain is made up of two layers which are separable up to the
eighth or tenth year. The external layer constitutes the endos-
teum of the cranial bones. It is their nutrient membrane.
Through the cranial foramina and sutures it is continuous with
the external periosteum. In the adult the internal layer of the
dura separates from the outer layer only over the apex of the
petrous bone, to form Meckel's space for the semilunar ganglion
(Gasseri); at the foramina, to form sheaths for the nerves; and,
along the sinuses, to form their internal boundary and to produce
the great incomplete partitions, called process.es, which project
centrally into the great fissures of the brain.

Processes. (Processus dura malris). From the inner surface
of the dura the great processes are given off. The falx cerebri

2 THE MENINGES OF THE BRAIN.

and falx cerebelli hang vertically in the longitudinal fissure of
the cerebrum and the posterior notch of the cerebellum; and,
into the transverse fissure of the cerebrum, extends horizontally the
tentorium cerebelli. The falx cerebri (Figs, i, and 4) is attached
in front to the crista galli -and behind to the internal occipital pro-
tuberance and superior surface of the tentorium; the falx cere-
belli (Fig. i) continues from the inferior surface of the tentorium,
along the occipital crest, to the posterior border of the foramen
magnum. The bony attachment of the tentorium cerebelli
(Fig. 2) is to the internal protuberance and the lateral arms of
the crucial ridge forward to the petrous bone; and, then, it is
along the superior border of the petrous bone to the clinoid proc-
esses of the sphenoid. Between its clinoid attachments there is
a deep bay, the incisura tentorii, which transmits the midbrain.
The diaphragma sellae is a small centrally perforated sheet of
dura which covers the hypophyseal fossa.

Sinuses. (Sinus durce matris). Large venous passages lined
with endothelial cells, and called sinuses, are situated between
the layers of the dura (Figs, i, 2, 3 and 4). In the convex and in
the free border of the falx cerebri are, respectively, the superior
sagittal sinus (s. sagittalis superior) and the inferior sagittal
sinus (s. sagittalis inferior). The superior (Fig. i) extends
from the foramen caecum back to the confluens sinuum (torcular
Herophili,) located at the internal occipital protuberance. Having
run through the posterior two-thirds of the concave border of
the falx cerebri, the inferior sagittal sinus joins the great cerebral
vein at the margin of the tentorium and forms the straight sinus
(s. rectus). The latter runs through the middle of the tentorium
to the confluens (Fig. 2). The occipital sinus (s. occi pit alls)
traverses the falx cerebelli from the foramen magnum upward
to the same point. In the confluens sinuum the transverse
sinuses (s. transversi) rise (Fig. 2). Grooving the horizontal
arms of the crucial ridge, each runs outward in the tentorium to
the base of the petrous bone, where it receives the superior petrosal
sinus; it then turns downward through the sigmoid fossa, com-
municates with the occipital sinus and unites with the inferior
petrosal sinus in the jugular foramen. Situated on either side

THE DURA MATER OF THE BRAIN. 3

of the sella Turcica is a continuation of the ophthalmic vein,
the large cavernous sinus (s. cavernosus) (Fig. 3), which receives
at the sphenoidal fissure the spheno-parietal sinus (s. ala> parva),
the course of which is along the posterior border of the lesser